Results 1 - 10 of 9566
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[en] In this study, fluorite structured oxides are used in numerous applications and as such it is necessary to determine their materials properties over a range of conditions. In the present study we employ molecular dynamics calculations to calculate the elastic and expansivity data, which are then used in a thermodynamic model (the cBΩ model) to calculate the activation volumes of oxygen self-diffusion coefficient in ThO_2, UO_2 and PuO_2 fluorite structured oxides over a wide temperature range. We present relations to calculate the activation volumes of oxygen self-diffusion coefficient in ThO_2, UO_2 and PuO_2 for a wide range of temperature (300–1700 K) and pressure (–7.5 to 7.5 GPa).
[en] Thin films of magnetic garnet materials, e.g. yttrium iron garnet (Y3Fe5O12, YIG), are useful for a variety of applications including microwave integrated circuits and spintronics. Moreover, substitution of rare earth ions, such as cerium, is known to enhance the magneto-optic Kerr effect (MOKE) as compared to pure YIG. Thin films of Ce0.75Y2.25Fe5O12 (Ce:YIG) have been grown using the pulsed laser deposition (PLD) technique and their crystal structure examined using high resolution scanning transmission electron microscopy. Homogeneous substitution of Ce in YIG, without oxidation to form a separate CeO2 phase, can be realized in a narrow process window with resulting enhancement of the MOKE signal. We investigated the thermally generated signal due to spin Seebeck effect for the optimally doped Ce:YIG films.
[en] By now it is known that in an s-wave superconductor-ferromagnet-superconductor (SF S) structure the supercurrent induced by spin singlet pairs can only transmit a short distance of the order of magnetic coherence length. The long-range supercurrent, taking place on the length scale of the normal metal coherence length, will be maintained by equal-spin triplet pairs, which can be generated by magnetic inhomogeneities in the system. In this paper, we have shown an unusual long-range supercurrent, which can take place in clean junction with non-parallel orientation of magnetic moments. The mechanism behind the enhancement of Josephson current is provided by the interference of the opposite-spin triplet states deriving from and interfaces when both ferromagnetic layers have the same values of the length and exchange field. This discovery can offer a natural explanation for recent experiments (Robinson et al 2010 Phys. Rev. Lett. 104 207001; Baek et al 2014 Nat. Commun. 5 3888). (paper)
[en] We studied the photoluminescence line shapes of free and bound excitons in a n-modulation doped –GaAs heterostructure with linearly increasing electric field in the p-doped buffer. At small laser excitation power the line shapes of the neutral donor bound and free excitons deviate strongly from a simple Lorentzian, whereas the neutral acceptor bound exciton is not obviously affected. Asymmetric lines of sawtooth-type form are observed for the donor bound and the free exciton. The line asymmetry could be traced back to the field dependent exciton binding energy and the field distribution in our heterostructure. A simple analytical model can account for the field dependent line shapes and a fit to the experimental lines gives a satisfactory agreement. (paper)
[en] We propose and theoretically demonstrate that two-dimensional materials at the interface between glass and water layers in a total internal reflection fluorescence microscopy (TIRFM) technique can decrease the detection volume of a target sample, and hence improve the resolution of the obtained image. In particular, we calculate the change in fluorescence characteristics of the fluorophore labels on a target sample when monolayer black phosphorus, hexagonal boron nitride, and graphene are added at the glass-water interface of a TIRFM structure. We also calculate the change in the detection volume due to the presence of two-dimensional materials, and when the polarization, wavelength, and angle of the incident light vary. We find 10% and 5% decrease in the detection volume when monolayer black phosphorus and hexagonal boron nitride are used, respectively, and up to ∼50% decrease when monolayer graphene is used. The proposed use of the two-dimensional material will significantly improve the resolution of TIRFM technique, and hence facilitate the study of nanoscale biological features. (paper)
[en] We study the optical and electrical properties of silver films with a graded thickness obtained through metallic evaporation in vacuum on a tilted substrate to evaluate their use as semitransparent electrical contacts. We measure their ellipsometric coefficients, optical transmissions and electrical conductivity for different widths, and we employ an efficient recursive method to calculate their macroscopic dielectric function, their optical properties and their microscopic electric fields. The topology of very thin films corresponds to disconnected islands, while very wide films are simply connected. For intermediate widths the film becomes semicontinuous, multiply connected, and its microscopic electric field develops hotspots at optical resonances which appear near the percolation threshold of the conducting phase, yielding large ohmic losses that increase the absorptance above that of a corresponding homogeneous film. Optimizing the thickness of the film to maximize its transmittance above the percolation threshold of the conductive phase we obtained a film with transmittance T = 0.41 and a sheet resistance . We also analyze the observed emission frequency shift of porous silicon electroluminescent devices when Ag films are used as solid electrical contacts in replacement of electrolytic ones. (paper)
[en] In this paper, ZnO with a novel hierarchical nanostructure has been synthesized by a new solution method. The novel hierarchical structure is named a ‘brush pen’. The biocompatibility and antibacterial properties of ZnO brush pens have been evaluated. The results demonstrate that ZnO brush pens show good antibacterial activity against Staphylococcus aureus. (paper)
[en] Co_xZn_1_−_xO (X = 0.20, 0.86, 0.92) films were synthesized using the radio frequency (RF) co-sputtering method. Though the same synthesis method was used, these samples exhibited different structures and magnetic properties. The Co_0_._2_0Zn_0_._8_0O film sample was crystalline, but its magnetic property was antiferromagnetism. Amorphous phase, room temperature ferromagnetism and anomalous Hall effect were shown in the sputtered and annealed Co_0_._8_6Zn_0_._1_4O and Co_0_._9_2Zn_0_._0_8O samples. Through x-ray photoelectron spectroscopy (XPS), the ferromagnetism of the high Co content amorphous films originates from metallic Co. The antiferromagnetism of Co_0_._2_0Zn_0_._8_0O crystalline film can be explained by an indirect-exchange interaction model. The electric conductivity is interpreted with the spin-dependent variable-range hopping model at low temperature. A tunneling magnetoresistance (TMR) ratio of 16.4% was observed at 77 K in Co(40 nm)/ZnO(4 nm)/Co_0_._9_2Zn_0_._0_8O(75 nm) magnetic tunnel junctions (MTJs). The MTJs can resist up to room temperature with the TMR ratio of 1.6% at 10 kOe. (paper)
[en] In this paper, we report on annealing temperature dependence of structural and electrical properties of the Sb_2Te and GeInSbTe thin films. X-ray diffraction shows an amorphous phase for the as-deposited films, while single crystalline hexagonal Sb_2Te phase for Sb_2Te films and mixed crystalline phases (rhombohedral Sb, cubic In_2Te_3 and hexagonal Sb_2Te) for the GeInSbTe films annealed above 150 °C. X ray reflectivity and room temperature resistivity measurements of the annealed films revealed the higher thermal stability of the GeInSbTe than Sb_2Te thin films at higher annealing temperatures. The electrical and optical measurements showed the minor role of the grain boundary scattering to the charge transport in both type of films. However, increase in annealing temperature lead to large increase in mobility of charge carriers in p-type films. This mobility improvement can be easily related to increase in scattering time of charge carriers attributed to better crystallization and thereby reduced scattering. The annealing of the Sb_2Te films above 225 °C results in partial evaporation of the material and increase in resistivity. (paper)
[en] We have studied weak localization (WL) and microwave-irradiated transport in multilayer graphene grown on SiC(0001). Different scattering channels are identified by analyzing the WL data. Moreover, we have shown that at a fixed ambient temperature, irradiating graphene with a microwave appears to be equivalent to changing the ambient temperature without microwave. We find that both the zero-field resistance of graphene and the WL correction term can be used as reliable thermometers which agree well with each other. (paper)